Field of the Invention
The present invention relates generally to spinal implant procedures and tools, and particularly to a procedure and tools for implanting facet joint screws percutaneously.
Discussion of the Known Art
U.S. Pat. No. 7,717,919 discloses a mechanical alignment jig (see FIGS. 17-20) for aligning the axis of an external cannula guide block to coincide with, or run parallel to, a determined internal target path along which a screw is to be delivered percutaneously to either one of two facet joints at a given level of a patient's spine. Each internal guide path is initially determined by a surgeon using conventional imaging means and by inserting markers.
Further, U.S. Patent Application Pub. No. 2010/0023018 describes a bilateral drilling guide (see FIG. 1) that is fixed by a clamp on the spinous process of a vertebral body in a patient's spine. An extension is mounted to extend laterally from the spinous process, and to rotate 180 degrees between either side of the vertebral body. A pointing device, a protractor, and a drill bushing are mounted on the extension to enable a number of drilling axes to be defined toward the body.
U.S. Pat. No. 4,907,577 discloses a transpedicle drill jig having a pair of drill guiding sleeves (see FIGS. 3-6) the distal ends of which can be placed at desired positions on either side of a vertebral body of a patient's spine. In use, the jig is held against but is not fixed to the vertebral body.
New products for facet fixation have been offered to complement the use of unilateral pedicle screws or stand-alone cages in spinal surgery. Many of these products do not fixate rigidly, and/or they are cumbersome to implant properly. Problems have been encountered mainly in the process of targeting and placing the screws in the patient's spine, rather than in fixation where conventional facet screws have proven to achieve the best results.
To achieve a minimally invasive spinal fusion procedure, surgeons may implant pedicle screws unilaterally by exposing the spine only at the side in which the screws are to be inserted, and provide contralateral facet joint fixation by use of facet screws inserted percutaneously with the aid of X-ray imaging and/or other navigation equipment. Notwithstanding the known art, there is a need for tool or system that will enable a surgeon to determine a first drilling axis along which a facet screw can be inserted percutaneously and accurately into a given side of a patient's spine, based only on the geometry of a second drilling axis determined at the opposite side of the spine, and without a need for X-ray or other navigation techniques. Such a tool could substantially reduce the time required to implant facet screws or other devices percutaneously at the given side of the spine.